From 18d7574ae297a24d53fe418e9008e969c29ffba2 Mon Sep 17 00:00:00 2001
From: Andrew Clark <git@andrewclark.io>
Date: Mon, 7 Dec 2020 13:10:53 -0600
Subject: [PATCH] Remove `catch` from Scheduler build (#20396)

Makes debugging errors harder.

In this case, we can use `finally` instead.
---
 packages/scheduler/src/forks/SchedulerDOM.js  | 24 ++++++++++-------
 .../src/forks/SchedulerPostTaskOnly.js        | 26 +++++++++++--------
 2 files changed, 29 insertions(+), 21 deletions(-)

diff --git a/packages/scheduler/src/forks/SchedulerDOM.js b/packages/scheduler/src/forks/SchedulerDOM.js
index 53101a6e6e58..e872b3ae6590 100644
--- a/packages/scheduler/src/forks/SchedulerDOM.js
+++ b/packages/scheduler/src/forks/SchedulerDOM.js
@@ -519,21 +519,25 @@ const performWorkUntilDeadline = () => {
     // the message event.
     deadline = currentTime + yieldInterval;
     const hasTimeRemaining = true;
+
+    // If a scheduler task throws, exit the current browser task so the
+    // error can be observed.
+    //
+    // Intentionally not using a try-catch, since that makes some debugging
+    // techniques harder. Instead, if `scheduledHostCallback` errors, then
+    // `hasMoreWork` will remain true, and we'll continue the work loop.
+    let hasMoreWork = true;
     try {
-      const hasMoreWork = scheduledHostCallback(hasTimeRemaining, currentTime);
-      if (!hasMoreWork) {
-        isMessageLoopRunning = false;
-        scheduledHostCallback = null;
-      } else {
+      hasMoreWork = scheduledHostCallback(hasTimeRemaining, currentTime);
+    } finally {
+      if (hasMoreWork) {
         // If there's more work, schedule the next message event at the end
         // of the preceding one.
         port.postMessage(null);
+      } else {
+        isMessageLoopRunning = false;
+        scheduledHostCallback = null;
       }
-    } catch (error) {
-      // If a scheduler task throws, exit the current browser task so the
-      // error can be observed.
-      port.postMessage(null);
-      throw error;
     }
   } else {
     isMessageLoopRunning = false;
diff --git a/packages/scheduler/src/forks/SchedulerPostTaskOnly.js b/packages/scheduler/src/forks/SchedulerPostTaskOnly.js
index ba081d3236e5..8ee96e2d16e5 100644
--- a/packages/scheduler/src/forks/SchedulerPostTaskOnly.js
+++ b/packages/scheduler/src/forks/SchedulerPostTaskOnly.js
@@ -512,21 +512,25 @@ const performWorkUntilDeadline = () => {
     // the message event.
     deadline = currentTime + yieldInterval;
     const hasTimeRemaining = true;
+
+    // If a scheduler task throws, exit the current browser task so the
+    // error can be observed.
+    //
+    // Intentionally not using a try-catch, since that makes some debugging
+    // techniques harder. Instead, if `scheduledHostCallback` errors, then
+    // `hasMoreWork` will remain true, and we'll continue the work loop.
+    let hasMoreWork = true;
     try {
-      const hasMoreWork = scheduledHostCallback(hasTimeRemaining, currentTime);
-      if (!hasMoreWork) {
+      hasMoreWork = scheduledHostCallback(hasTimeRemaining, currentTime);
+    } finally {
+      if (hasMoreWork) {
+        // If there's more work, schedule the next browser task at the end of
+        // the preceding one.
+        postTask(performWorkUntilDeadline);
+      } else {
         isTaskLoopRunning = false;
         scheduledHostCallback = null;
-      } else {
-        // If there's more work, schedule the next message event at the end
-        // of the preceding one.
-        postTask(performWorkUntilDeadline);
       }
-    } catch (error) {
-      // If a scheduler task throws, exit the current browser task so the
-      // error can be observed.
-      postTask(performWorkUntilDeadline);
-      throw error;
     }
   } else {
     isTaskLoopRunning = false;